The aim of this study is to identify those processes by which afferent sensory information regulates cerebral development, and thus modifies the potential of the brain. The visual system of the chick offers an ideal experimental model in which to dissect out various parameters and identify their individual contributions. In previous studies we have shown that the metabolism of cerebral macromolecules is promptly reduced by monocular visual deprivation and that this effect may be mediated by the vascular system. It is planned to examine cerebral blood flow and the status of the blood- brain barrier in young chicks receiving a different visual input into each eye. We will look for selective changes in the penetrability of substances into the brain and for asymmetry of data from paired brain regions of each bird. We will examine the extent to which any impairments found can be reversed. Such relatively short-term changes may lead to more permanent morphological variations and thus ultimately determine the characteristic behavior of an organism. We also propose to study the development and extent of and possible physiological modulation of the distal axoplasmic transport of materials in the optic pathway.